It is known that individuals have different propensity to move either their eyes or their head when successively looking in different directions.
Such propensity can be of importance when producing ophthalmic lenses.
For example, as disclosed in US Publication No. 2010/0002191, such propensity can be taken into account in order to determine a compromise between the correction of the foveal vision and that of the peripheral vision when producing an ophthalmic lens.
For a wearer who prefers to move his eyes in order to view an off-axis object, the lens manufacturer may provide an ophthalmic lens having a larger zone of the ophthalmic lens that corrects the wearer's foveal vision. Thus, the image of an object viewed by the wearer is correctly formed on the retina, for a greater interval of the angle of rotation of the eyes.
Whereas, for a wearer who prefers to move his head, and thus who usually looks through the ophthalmic lens in a restricted zone located around the centre of the ophthalmic lens, a larger peripheral zone is adapted for the peripheral vision.
International Publication No. WO2009/044080 discloses a method of adapting the addition values of the anterior and posterior faces of a progressive ophthalmic lens not only so as to obtain substantially the addition value of the ophthalmic lens that is prescribed but also to adapt a feature of use of the ophthalmic lens according to the eye and head movements of the wearer.
This adaptation of the feature of use of the progressive ophthalmic lens corresponds to a customization of the progressive ophthalmic lens. It is carried out in order to improve a sensation of the wearer that occurs when he changes his sight direction. In this way, an increased comfort and use of the progressive ophthalmic lens is obtained.
As illustrated with the previous examples, since the propensity to move either the eyes or the head becomes an important parameter when designing a progressive ophthalmic lens, it is important to provide methods for determining the relative amplitude of eye and head movements of an individual that are more and more precise.
The inventors have observed that the known “head/eye” movement coordination tests turn out to present precision defects.
The discussion of the background of the invention herein is included to explain the context of the invention. This is not to be taken as an admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of any of the claims.